Methylpentacarbonylmanganese and diethylselenium have been pyrolyzed for the organometallic chemical vapour deposition of manganese selenide thin films. Polycrystalline layers of manganese selenide exhibiting either rocksalt structure or both rocksalt and zincblende structure have been fabricated. The structure is related to substrate temperature. In addition, we report on the thermal stability of the methylpentacarbonylmanganese precursor. High cracking temperatures lead to the formation of manganese oxide instead of breaking the manganese-carbon bond. Moreover, we point out that the formation of carbonylselenide might be a parasitic reaction when cracking simultaneously methylpentacarbonylmanganese and diethylselenium. © 1998 Elsevier Science B.V. All rights reserved.