A semiconductor acceleration sensor of a single integral type has a semiconductor substrate, a first nitride layer, a first poly-silicon layer, a second nitride layer, a second poly-silicon layer, a third nitride layer and a third poly-silicon layer which are fabricated in order. A movable section is formed in a part of the second poly-silicon layer placed in a cavity enclosed and sealed by the first nitride layer, the first poly-silicon layer, the second nitride layer, the second poly-silicon layer, the third nitride layer and the third poly-silicon layer. A fabrication method of the semiconductor acceleration sensor of a single integral type is also disclosed.