We have developed an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) designed to work in conjunction with a commercial, high-vacuum scanning electron microscope (SEM). The STM resides in its own UHV subchamber which is housed in the JEOL 820 SEM. We have used the SEM to image the STM tip and its location on the sample. This instrument was built to fabricate and study metallic and contamination resist nanostructures and devices on semiconductor surfaces. To create these structures, we use a technique developed in our lab which uses the STM to dissociate organometallic gases or organic residues on semiconductor surfaces. Our system allows precise alignment of the STM-fabricated structures with underlying macroscopic contact pads. The UHV subchamber, which includes standard UHV sample preparation and analysis equipment, is required to prepare atomically flat and clean samples.