A selective dry etching technique for II-VI semiconductors based on ZnSe has been developed by using thermally assisted electron cyclotron resonance etching with a gas mixture of Ar, Cl-2, and BCl3. While the etching process is found to be almost nonselective between ZnSe and MgZnSSe at low (< 100 degreesC) and high (> 220 degreesC) substrate temperatures, a strong selectivity is obtained in the intermediate temperature range (e.g., 12:1 for; T-sub = 180 degreesC). Due to the ultrahigh vacuum (UHV) design of the etching chamber, a complete in situ fabrication of buried II-VI nanostructures should be accessible.