We designed and built a combination of a scanning tunneling microscope (STM) and a scanning electron microscope (SEM) which is working under ultrahigh vacuum conditions (base pressure typically 7 cdot 10⁻¹¹ mbar). The SEM is ideally used for surveying the sample and to control the STM tip positioning, while the STM extends the resolution range into the atomic scale. The design concept allows moving the STM tip freely over the sample under SEM control and using both imaging techniques simultaneously. The system is equipped with an electron energy analyzer (cylindrical sector analyzer) providing Auger electron spectroscopy, scanning Auger microscopy (SAM) and x-ray photoelectron spectroscopy capabilities. In addition, low energy electron diffraction and reflection high energy electron diffraction facilities are installed. In order to use these very different imaging techniques in situ, several special solutions had to be incorporated in the design of the system; they are described in detail. Some results are presented which demonstrate the performance of the STM/SEM system. Atomic resolution of the STM, a SEM resolution of up to 20 nm, and a SAM resolution of better than 100 nm were achieved.