  The valence band edge in tiny angle twist bilayers of MoS$_2$ and phosphorene
is shown to consist of highly localized energy levels created by a `moir\'e
quantum well', i.e. trapped by the interlayer moir\'e potential. These
approximately uniformly spaced energy levels exhibit a richly modulated charge
density, becoming ultra-localized at the valence band maximum. The number and
spacing of such levels is controllable by the twist angle and interlayer
interaction strength, suggesting the possibility of `moir\'e engineering'
ordered arrays of quantum dots in 2d twist semi-conductors.
