To obtain a semiconductor inertia sensor which does not require laser beam machining operation, which is suitable for high volume production and which is low in cost and to obtain a semiconductor inertia sensor whose parasitic capacitance is low, whose interelectrode-gap formation accuracy is good and whose sensitivity and accuracy are high.

In a semiconductor inertia sensor 30, a moving electrode 26 which is composed of single-crystal silicon is formed so as to be levitated at the upper part of a glass substrate 10, and one pair of fixed electrodes 27, 28 which are composed of single-crystal silicon are installed so as to sandwich the moving electrode 26. The base end part of a beam which supports the moving electrode 26 is installed on the glass substrate 10 via a spacer layer 23a composed of single-crystal silicon whose crystal face orientation is different from that of the single-crystal silicon.