The present disclosure relates to semiconductor structures and, more particularly, to a slot assisted grating based transverse magnetic (TM) pass polarizer and methods of manufacture. The structure includes: a waveguide strip composed of a first type of material and having openings along its length which are positioned to reflect/scatter a propagating electromagnetic waves; and grating fin structures on one or both sides of the waveguide strip which are positioned and structured to reflect/scatter the propagating electromagnetic waves.