The realization of high performance GaN normally-off power switching device is a hotspot in present study. Trench gate MOSFET is attractive for its large gate voltage swing and low gate leakage current. The trench gate structure is commonly formed by etch method which will introduce defect at metal-oxide-semiconductor (MOS) channel. First, the selective area growth (SAG) technique is proposed to realize trench gate normally-off MOSFET for the purpose of avoiding defect at gate channel in this paper. Then through the improvement of SAG technique including separating the SAG interface and hetero-interface and suppressing the background doping, high quality AlGaN/GaN heterostructure is regrown. The research result shows that SAG technique can retain the smooth surface in gate channel leading to superior threshold voltage stability which demonstrates SAG technique as the promising way for fabricating high performance trench gate normally-off MOSFET.