temporary layers as shown in fig3 b the temporary layer 31a which is the lower layer of the first temporary layer 31 is first removed with an organic solvent such as acetone the constituent material of the insulating film 18 such as sio 2 satisfactorily resists organic solvents and thus no particular problems are presented even in cases where it is immersed in an organic solvent for a long time a clearance 32 is formed in this way a strongly alkaline aqueous solution then permeates through the clearance 32 here since the strongly alkaline aqueous solution rapidly permeates through the clearance 32 which enlarges as the lower layer 31b of the first temporary layer 31 is dissolved the second and the third temporary layers 22 23 may be removed in a short time the insulating film 18 being not damaged by the long local exposure to the aqueous solution of the alkali serves to increase the reliability of the resulting device fig4 through fig9 illustrate a method of forming the ink jet head shown in fig1 according to a third embodiment of the invention the process according to the third embodiment proceeds in the order a through p fig4 fig6 and fig8 illustrate cross sectional views taken along the section line y y shown in fig1 and fig5 fig7 and fig9 illustrate cross sectional views taken along the section line x x in fig1 respectively the portions corresponding to those according to the first and the second embodiments are indicated by the same reference numerals for simplicity of explanation according to the.