We have investigated new quaternary solid solution semiconductor Pb1-x(Mg1-xSry)(x)S (x<0.1) thin films which have been fabricated on a BaF2 (111) substrate by using hot-wall epitaxy. It has been found that the energy band gap can be controlled desirably under keeping the lattice constant and monitoring the growth conditions. The properties of the optical absorption edge observed are suggestive of a direct energy band gap structure. The Hall mobility for the films changes monotonically from 4423 to 337 cm(2)/V s at 77 K with increasing x. The full-width at half-maximum of the films lattice-matched to PbS increases from 133 to 208 arcsec in proportion to x under the lattice misfit of 4.3% between the film and the BaF2. (C) 2002 Elsevier Science B.V. All rights reserved.