We present a new technology that uses the selective generation and etc
hing of porous silicon. This technology combines the advantages of sur
face micromachining (small area consumption, CMOS compatibility, front
side lithography) with the advantage of bulk micromachining (large di
stance, no sticking). The practical application is shown in two exampl
es: a free-standing polysilicon bridge for flow measurement and a thin
-film sensor for a thermal transducer.