The 'exciton gas-plasma' transition (the Mott transition) in a Si{sub 0.93}Ge{sub 0.07}/Si thin quantum well is investigated using low-temperature photoluminescence. It is demonstrated that this transition is smooth and occurs in the concentration range from approximately 6 x 10{sup 10} to 1.2 x 10{sup 12} cm{sup -2}. At a temperature of 23 K and excitation densities of higher than 10 W/cm{sup 2}, the shape and location of the luminescence line associated with the electron-hole plasma remain unchanged with an increase in the pump density. This can indicate the occurrence of an 'electron-hole gas-liquid' transition. It is shown that, in the spectrum of the quantum well, the luminescence of boron-bound excitons dominates at liquid-helium temperatures and low excitation densities, whereas the free-exciton luminescence dominates at temperatures above 10 K. The influence of the homogeneous and inhomogeneous broadening on the electron-hole plasma and exciton luminescence is discussed.