Field-effect transistors are fabricated from the Si/Si1−xGex heterostructures. The density of the two-dimensional electron system (2DES) in the strained Si quantum well can be controllably tuned from 2.13×1011 to 4.24×1011 cm−2. The temperature dependence of the resistivity of the 2DES was measured and the apparent metal–insulator transition was observed. Its main features are similar to those reported in other semiconductor-based two-dimensional systems.