Results are presented on our efforts in the patterning of Si wafers without using photoresist. The process is similar to the recently reported surface modification of GaAs with ultraviolet (UV) light to produce a stable mask surface. However, in the absence of an easily modifiable surface oxide on Si, a hydrogen-passivated and oxide-free Si surface is exposed to UV light in the presence of oxygen to form an oxide in the irradiated regions. Selective Si growth and etching were demonstrated on wafers so patterned, and preliminary results showing the promise of this technique are reported in this letter. © 1999 American Institute of Physics.