We measured the torsion of a small scanning force microscope cantilever beam that is induced by the lateral force acting on its tip during the scanning across a sample surface. The detection is based on the piezoresistive principle. Two resistor loops are suitably arranged on the beam and sense differences in the stress distribution. The silicon cantilever has a spring constant of k/sub b/ = 2.7 N/m, a torsional rigidity of k/sub t/ /spl equiv/ 5000 N/m and a resonant frequency of 40 kHz. The integrated silicon tip has a length of 6 /spl mu/m. The torsional sensitivity of the device is demonstrated by imaging in friction mode a grating of 15 nm in height, yielding an amplified (G=2000) output signal of 300 mV.