my father died and left everything to my step mom, as first first born am i entitled to anything i have e half brothers

When you state that your father left the remainder of his estate to your step-mother, it appears that he did so by Will or through a Living Trust. A spouse can take an elective share and prevent being cut out of a Will but a child does not have an entitlement to be a beneficiary of an estate. The exception is If any part of a Pennsylvania decedent's estate is not effectively disposed of by Will or Living Trust, the remainder will be distributed in the following order and manner:

1. Surviving spouse. A surviving spouse is generally first in line. The amount varies as follows:

A surviving spouse is entitled to the entire intestate estate if the decedent is not survived by a child or parent.
If there are no surviving children of the decedent, but there is a surviving parent or parents, the surviving spouse is entitled to the first $30,000 plus one-half of the remaining intestate estate. There is an exception to this rule if a decedent died due to the September 11, 2001, terrorist attacks, in which case the surviving spouse gets 100 percent of any compensation award paid under the Air Transportation Safety and System Stabilization Act.

If the decedent is survived by children all of whom are also the children of the surviving spouse, the surviving spouse is entitled to the first $30,000 plus one-half of the remaining intestate estate.

If the decedent is survived by children one or more of whom are not issue of the surviving spouse, the surviving spouse gets one-half of the intestate estate.

When there is a partial intestacy, any property received by the surviving spouse under the Will counts toward satisfying the $30,000 allowance mentioned above.

2. Heirs other than surviving spouse. Any part of the intestate estate not passing to the surviving spouse as indicated above, or the entire intestate estate if there is no surviving spouse, passes as follows to:

Decedent's issue.
Decedent's parent or parents equally.
Decedent's brothers and sisters, or their issue.

If none of the above relatives are available, but the decedent is survived by one or more grandparents or issue of grandparents, half of the estate passes to the paternal grandparents if both survive, or to the surviving paternal grandparent or to the issue of the paternal grandparents if both are deceased. The other half passes to the maternal relatives in the same manner. If there is no surviving grandparent or issue of grandparent on either the paternal or maternal side, the entire estate passes to the relatives on the other side in the same manner as the half portion would.

Decedent's uncles and aunts and their children and grandchildren.

3. Commonwealth of Pennsylvania. If there is no taker under any of the above provisions, the intestate estate passes to the commonwealth of Pennsylvania.