In this paper the electrodynamical characteristics of open microstrip lines (MSLs) with semiconductor n–Si substrates were investigated using the method of singular integral equations (SIE) in the quasi–TEM approximation. Our algorithm allows anyone to consider in their calculations the real geometry and sizes of MSLs. There is an agreement between our numerical and experimental results. The dependences of a complex wave impedance, a wavelength, and an attenuation constant of a MSL were analyzed on the frequency ƒ until ƒ = 70 GHz. Our calculations were fulfilled for MSLs with low ohmic semiconductor substrates and for several specific resistivities of the substrate material. We specified the dependences of electrodynamical characteristics on frequencies when they became constant at the start of a certain frequency and then they remained constant at higher frequencies. These frequency values were dependent on the substrate specific resistivity.