Three new arboreal theraphosid spiders of the genus Phormingochilus Pocock, 1895 are here described from Sulawesi and Sarawak, Borneo: Phormingochilus carpenteri sp. nov., P. kirki sp. nov., and P. pennellhewletti sp. nov. The genus has been revised and historical species redescribed. The authors have also discussed the placement of the Ornithoctoninae genera Cyriopagopus Simon, 1887, Lampropelma Simon, 1892 and Omothymus Thorell, 1891 and, after an examination of the type material, concluded that Cyriopagopus is a senior synonym of the genus Haplopelma Simon, 1892 and that the genus Omothymus needs to be restored to house the arboreal Malaysian mainland species schioedtei (Thorell, 1891) and thorelli (Simon, 1901), which were formerly assigned to the genus Cyriopagopus but have now been restored to their original placement. We have also concluded, on examination of the type material that the female of Lampropelma violaceopes Abraham, 1924 from Southern Malaysia should be removed from the genus Lampropelma (whose distribution at present, we believe to be limited to Lampropelma nigerrimum from Sangihe (Sangir) Island) and placed in the genus Omothymus, whereas the male, from Penang, is deemed to be a misidentified specimen of Cyriopagopus (Omothymus) schioedtei.