The structure of a molecule of $N(SiM{e}_3{)}_3$ is :

When left outside in the open, $N(SiM{e}_3{)}_3$ feels waxy to the touch. The solid-state structures of these compounds have been determined by single-crystal X-ray diffraction studies.$N(SiM{e}_3{)}_3$ has a twisted core nitrogen atom that displays approximately trigonal planar coordination.
Due to back bonding, nitrogen hybridization is sp².