Abstract: This invention is concerned with the production of glasses especially suitable for the encapsulation of semiconductor devices and, in particular, for the encapsulation of germanium and silicon diodes. The glasses have a low softening point, i.e., less than about 550.degree. C., are readily sealable to Dumet, and exhibit a viscosity at the liquidus of at least 20,000 poises. The glasses have compositions within the K.sub.2 O-PbO-B.sub.2 O.sub.3 -SiO.sub.2 system, are essentially free from Li.sub.2 O, Na.sub.2 O, Al.sub.2 O.sub.3, and TiO.sub.2, and demonstrate a mismatch in thermal expansion with Dumet at about 400.degree. C. of no more than about 200 PPM.