A method for forming a transistor including a self aligned metal gate is provided. According to various method embodiments, a high-k gate dielectric is formed on a substrate and a sacrificial carbon gate is formed on the gate dielectric. Sacrificial carbon sidewall spacers are formed adjacent to the sacrificial carbon gate, and source/drain regions for the transistor are formed using the sacrificial carbon sidewall spacers to define the source/drain regions. The sacrificial carbon sidewall spacers are replaced with non-carbon sidewall spacers, and the sacrificial carbon gate is replaced with a desired metal gate material to provide the desired metal gate material on the gate dielectric. Various embodiments form source/drain extensions after removing the carbon sidewall spacers and before replacing with non-carbon sidewall spacers. An etch barrier is used in various embodiments to separate the sacrificial carbon gate from the sacrificial carbon sidewall spacers. Other aspects and embodiments are provided herein.