Chemoselective hydrosilylation of amides to hemiaminals offers an effective route to aldehydes and nitrogenous skeletons. We herein present a KO^tBu-catalyzed hydrosilylation of various aromatic and aliphatic tertiary amides with TMDS affording aldehydes and/or functional amines with excellent chemoselectivities (up to 30 : 1) under mild and convenient conditions. Mechanistic investigations using in situ¹H/²⁹Si NMR and FTIR show the highly selective hemiaminal formation and reveal a rapid disproportionation of TMDS controlled by amides and KO^tBu. Moreover, the product of disproportionation, Me₂SiH₂, is confirmed as the distinctive reductant for the precise chemoselectivity control of hydrosilylation.