Below is a general discussion of inheritance rights for half-siblings in the Philippines, based on the Civil Code of the Philippines and related laws. This is not legal advice but a summary of common rules and principles. For specific cases, consulting a qualified attorney is always advisable.

1. Definition of Half-Siblings in Philippine Law

In Philippine law, “half-siblings” (also known as half-brothers or half-sisters) are siblings who share only one common parent:

Consanguine (same father, different mothers); or
Uterine (same mother, different fathers).

Legally, half-siblings are often referred to as “brothers and sisters of the half-blood,” in contrast to “full-blood siblings,” who share the same mother and father.

2. Governing Laws and Key Provisions

2.1 Civil Code of the Philippines (Republic Act No. 386)

Book III (On the Different Modes of Acquiring Ownership) Title IV (Succession).
- These provisions govern both testate (with a will) and intestate (no will) succession.
- The distinction between full-blood and half-blood siblings for purposes of inheritance is expressly found in the Civil Code.

Key articles relevant to siblings’ rights (especially in intestate succession) include:

Article 970 onwards: Defines who are collateral relatives.
Article 1001–1009: Enumerates general rules on intestate succession involving brothers and sisters, nephews, and nieces.
Article 1010: Provides that in intestate succession, a full-blood brother or sister is entitled to double the share of a half-blood brother or sister.

2.2 Family Code of the Philippines (Executive Order No. 209)

The Family Code superseded some provisions of the Civil Code regarding family relations (e.g., legitimacy of children, recognition of illegitimate children, etc.).
While it does not drastically alter the inheritance rules for half-siblings per se, it does clarify matters of legitimacy and filiation, which can affect whether a half-sibling is recognized as an heir.

3. Distinguishing Factors for Half-Siblings in Inheritance

3.1 Legitimacy or Illegitimacy of the Parties

Inheritance rights for siblings—whether half or full—can also be influenced by legitimacy status. However, in discussing half-siblings specifically:

Half-Siblings from Married Parents:
- If they are children from lawful marriages (i.e., recognized legitimate children of each parent), they are legitimate to their respective parents. But being “half-blood” siblings simply means they share only one parent in common.
Illegitimate Half-Siblings:
- If one or both siblings are illegitimate children of the parent they share, the principle remains that they have common blood from that one parent—provided that the illegitimate child is duly recognized under Philippine law (through appropriate legal recognition, voluntary or court-ordered).
- Recognition ensures the illegitimate child still has certain inheritance rights, though typically the child’s legitime from the parent is half of that of a legitimate child’s legitime. For siblings, the key point is the half-blood relationship remains a ground for inheritance rights—provided filiation is legally established.

3.2 Full-Blood vs. Half-Blood Shares in Intestate Succession

When a person dies without leaving a will (intestate succession), the surviving relatives inherit according to the order and rules set out in the Civil Code. Siblings are considered collateral relatives of the deceased.

Article 1010 of the Civil Code states that in intestate succession among brothers and sisters:

“Full-blood siblings shall each be entitled to double the share of half-blood siblings.”

For example:
- Suppose the estate (net inheritance) is PHP 300,000.
- There are 2 full-blood siblings (A and B) and 1 half-blood sibling (C).
Under Article 1010:
- A full-blood sibling = double the share of a half-blood sibling.
Let x = share of each half-blood sibling.
Then each full-blood sibling = 2x.

We have 2(2x) + x = 300,000 → 4x + x = 300,000 → 5x = 300,000 → x = 60,000.
- Half-blood sibling (C) = PHP 60,000.
- Each full-blood sibling (A and B) = 2x = 2 × 60,000 = PHP 120,000.

Hence, in the absence of a will and other heirs of closer degree (such as children or parents), half-siblings inherit, but each of them gets half the portion of a full-blood sibling.

4. Intestate Succession Scenarios Involving Half-Siblings

It is crucial to understand where half-siblings stand in the “order of intestate heirs.” According to the Civil Code:

Descendants (Children, Grandchildren) take priority over all other heirs.
Ascendants (Parents, Grandparents) come next if no descendants exist.
Surviving Spouse has a share in practically all scenarios unless there is a valid waiver or other disqualification.
Collateral Relatives (which include siblings) come into play only if there are no descendants or ascendants, or if they share the estate with the surviving spouse in certain situations prescribed by law.

Therefore, half-siblings typically inherit:

After the deceased’s legitimate or illegitimate children (and their descendants), and
After the deceased’s surviving parents (or ascendants),
Possibly together with a surviving spouse or in default of other heirs.

Example Scenario

Deceased dies unmarried, with no children, and both parents predeceased him:
- The intestate heirs may be his siblings.
- If he has 1 full-blood sibling and 1 half-blood sibling, the full-blood sibling receives double the share of the half-blood sibling under Article 1010.
Deceased leaves a surviving spouse and siblings (no children, no parents):
- Under Article 1001 of the Civil Code, if the deceased leaves a surviving spouse and siblings (of full or half-blood), the spouse gets half the estate, and the siblings get the remaining half. Within the siblings’ half, the full-blood sibling’s share is double that of the half-blood sibling.

5. Testate Succession (When There Is a Will)

If the decedent executes a valid will, the following considerations apply:

Forced Heirs:
- The law reserves certain “legitimes” for compulsory or forced heirs (i.e., children, legitimate parents, surviving spouse).
- Siblings—whether full-blood or half-blood—are not considered forced heirs under Philippine law. That means the testator can freely disinherit siblings (full or half) if they wish, or simply not give them anything in the will—provided no other mandatory rules (e.g., legitimes of children, spouse, or parents) are violated.
Free Portion:
- After satisfying the legitimes of forced heirs (if any), the testator is free to assign the remainder of the estate (the “free portion”) to anyone, including half-siblings, full siblings, strangers, or charities, in whatever proportion he or she wishes.
Legacy or Devise to Half-Siblings:
- A testator can choose to leave a specified portion or property to a half-sibling.
- Because siblings are not forced heirs, the decedent’s will can also omit them entirely.

6. Recognition of Half-Siblings (Establishing Filiation)

For a half-sibling to inherit from another half-sibling, filiation to the common parent must be legally established. This is most pertinent in the case of illegitimate children. Filiation can be established by:

Record of birth appearing in the civil register (and recognized by the father or mother);
Admission of filiation in a public or private document;
Judicial action for recognition (in cases where the alleged parent refuses acknowledgment).

Without proper recognition, the half-sibling who is illegitimate would lack legal standing as an heir. Thus, even if they share blood in fact, the law requires proof of that filiation for inheritance to arise.

7. Practical Considerations and Common Issues

Documentary Evidence:
- Birth certificates, family records, and court decisions are critical in proving relationships between half-siblings.
Legal Representation:
- If an acknowledged half-sibling predeceases the decedent, his or her children (the decedent’s nephews/nieces) could inherit by right of representation in intestate succession. This follows the rules for collateral relatives in the Civil Code (Articles 970, 1008, 1009).
Dangers of Assumption:
- Many families assume that half-siblings have no rights or that all siblings inherit equally. The law, however, clearly grants half-siblings the right to inherit in the absence of other closer heirs but at half the share of a full-blood sibling in intestate scenarios.
Illegitimacy and Reduced Share:
- The concept that “illegitimate children get half the share of legitimate children” applies with respect to inheritance from the parent. Between siblings themselves, the question of half-blood or full-blood is the controlling factor. However, if a half-sibling was never recognized by the common parent, a legal battle may ensue to establish the relationship.
Disinheritance:
- Because siblings are not forced heirs, they can effectively be disinherited if the decedent leaves a valid will that omits them or does not assign them anything.

8. Summary of Key Points

Half-siblings (half-blood) share only one parent in common.
In intestate succession, half-siblings inherit only if there are no closer heirs (e.g., children, parents) or they share with a surviving spouse when no descendants or ascendants exist.
Article 1010 of the Civil Code gives full-blood siblings double the share of half-blood siblings in intestate distribution.
Siblings—whether full-blood or half-blood—are not forced heirs in the Philippines, so they can be freely omitted in a will.
Filiation must be established for an illegitimate half-sibling to inherit.
Legal disputes often arise around documentary proof and recognition, especially for illegitimate half-siblings.

9. Conclusion

Inheritance rights for half-siblings in the Philippines center on the principle that they receive a share in the absence (or default) of forced heirs but at half the portion of a full-blood sibling under intestate succession. Because siblings are not forced heirs, a valid will can diminish or remove their share entirely. Finally, recognition or establishment of filiation is crucial for half-siblings born out of wedlock. Anyone facing an inheritance issue involving half-siblings is best advised to seek personalized legal counsel to navigate the specific facts and applicable legal procedures.