passive element that is one protruded portion of the passive element however it is apparent that mounting of a passive element having plural terminals can be performed when the number of recesses of the silicon substrate 1 and the number of protrusions of the passive element are increased in correspondence with the number of terminals of the passive element fig5 is a sectional view of an electronic circuit device having a silicon substrate according to embodiment 3 of the present invention the silicon substrate 1 has a front surface and a back surface the upper side of fig5 corresponds to the front surface and the lower side thereof corresponds to the back surface the elements such as a transistor resistor and capacitor are formed on the front surface of the silicon substrate 1 by using the silicon planar process a point of difference from the embodiment in fig3 is that the recess of the silicon substrate has two levels the shape of the recess thus eases the insertion of the passive element 2 from the front surface of the silicon substrate further as the shape of the recess a tapered shape can also be made by conducting taper etching through anisotropic wet etching and then conducting drie vertically as shown in fig6 this structure further eases the insertion of the passive element 2 from the front surface of the silicon substrate further fig7 is a sectional view of an electronic circuit device having a silicon substrate in the case where the shape of the passive element 2 has two levels in this case the terminals.