We describe the fabrication process of a two_dimensional silicon_based photonic crystal (PC) slab with partial air_bridge, which has a photonic band gap in the nearIR range .The process involves the formation of the air_bridge silicon slab by wet etching and the fabrication of periodic air holes by a focused ion beam. We successfully obtained such a sample and measured its transmission in a wide spectrum. It is found that the observed spectrum is consistent with the theoretical values calculated by the plane wave expansion method. The TM0_like modes reduce the size of the band gap, and the partial air bridge is beneficial to the fabrication of large PC slabs. Meanwhile, it is possible to draw light out from the supporting material of the air bridge.