Monocrystalline silicon wafers (c-Si) form the material base for the modern microelectronics industry. In recent years, c-Si has also become increasingly important as a mechanical material. The possibility of integrating electronic components into micromachined mechanical structures makes c-Si an increasingly interesting material for the fabrication of microsensor and microactuator devices. This paper presents a number of examples which demonstrate how thin films can be used in combination with micromachined silicon substrates or silicon wafers containing pre-fabricated electronic circuits. The examples presented include optoelectronic, integrated optic, mechanical, thermal and chemical sensor devices.