A plate-type heat exchanger is comprised of a stack of dished plates, with the plates being sealed at their margins by nesting sidewalls and the plate bottoms being spaced from one another to define a plurality of flow passages. Each of the plates has two pairs of openings. Two of the openings are formed in bosses which are joined to the sidewall along a portion of their length, thereby avoiding formation of a bypass channel between the bosses and the sidewall and maximizing the plate area available for heat transfer. The other two openings are provided with ribs which support the bosses of upwardly adjacent plates in the stack and which provide channels to provide transverse distribution of fluid across the plate.