Silicon monoxide (SiO) formed by molecular beam deposition (MBD) has many attractive optical, electrical, mechanical, and chemical properties which make it a suitable dielectric for many semiconductor device applications. It can be thermally evaporated at a much lower temperature than Si, SiO2 or Si3 N4 and it condenses on cooler surfaces in uniform and adherent stoichiometric SiO (x = 1) films when evaporated in high vacuum. At low deposition rates and at high pressures of oxygen, SiOx (1 ≤ x ≤ 2) films result. This allows variation of refractive index, stress and other properties of SiOx with x. In general, the SiO (x = l) films are under tensile stress <100 MPa which is significantly lower than that observed in other dielectric films. Slight introduction of oxygen during deposition reduces the tensile stress; at an O2 pressure of 5 × 10−7 Torr and above, the films are in compression. This allows the tunability of stress in SiOx films and deposition of films essentially free from stress. Furthermore, both Si and SiO have similar values of the linear thermal expansion coefficient (average values between 23 °C and 350°C: 3.37 × 10−6°C−1 and 2.7 × 10−6°C−1, respectively). As a result, SiOx/Si films develop little thermal stress during thermal cycling.