It is well established that during machining, materials with lower hardness presents higher ductility. However, in the machining of semiconductor crystals the brittle to ductile transition may not strictly follow this rule. This paper intends to show that the extent of the ductile response of monocrystalline semiconductors can not be related to its microhardness value, since the plastic behavior of semiconductor crystals is related to a phase transformation induced by pressure/stress. This was investigated by carrying out microindentation and single point diamond turning tests in three different semiconductors, InSb, GaAs and Si[001]-oriented single crystals. Based upon tests results it is observed that the onset of brittle behavior is brought forward to semiconductors with higher transition pressure value. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)