The present disclosure provides a semiconductor structure. The semiconductor structure includes a fin active region formed on a semiconductor substrate and spanning between a first sidewall of a first shallow trench isolation (STI) feature and a second sidewall of a second STI feature; an anti-punch through (APT) feature of a first type conductivity; and a channel material layer of the first type conductivity, disposed on the APT feature and having a second doping concentration less than the first doping concentration. The APT feature is formed on the fin active region, spans between the first sidewall and the second sidewall, and has a first doping concentration.