opposing walls and the face of the silicon wafer occur at the same rate a method of manufacturing a capacitance type acceleration detector in a silicon wafer using the aforementioned etching method application_number US 80615097 A description an embodiment of the present invention will be explained hereinafter with reference to the attached drawings when an anisotropic etching which employs a solution of koh is applied to a silicon wafer 110 etched conditions of the silicon wafer 110 by various kinds of concentrations of koh were observed that is when the concentration of koh was changed from 30 percent by weight to 45 percent by weight at the time of micromachining of the silicon wafer 110 the etched conditions of the silicon wafer 110 as shown in fig3 a to 3e were obtained as the observation results in sectional views of the wafer about a narrow gap portion having a width of 10 u03bcm and a very large gap portion an opening portion fig3 a to 3e are sectional views showing the etched conditions of the narrow gap portion gs and the opening portion gl with respect to the respective concentrations of koh namely to 30 percent by weight 35 percent by weight 37 5 percent by weight 40 percent by weight and 45 percent by weight that is 1 it can be understood that in the case of a concentration of koh being 30 percent by weight the etching to the face 110 proceeds substantially at the same speed in both the narrow gap portion gs and in the opening portion.