Is real estate transfer tax due between half-siblings?

hello everyone,
I am planning to buy a house from my half-sister (same mother).
We have already agreed on a sum.
My question now is whether I have to pay the real estate transfer tax when I buy the house or if it does not have to be paid because it is within the family.
I am grateful for any advice :-)

Short and concise yes the tax is due. There are a few exceptions, but these require that the property is gifted. Then the inheritance or gift tax is the decisive tax, which in turn has corresponding exemptions. Be happy about a reasonable purchase price and the fact that no realtor is involved and pay.