The tight‐binding method is applied, for the first time, to the analysis of the conduction‐band structure of GaAs‐Al0.4Ga0.6As quantum wires which are parallel to the [110] orientation. The results indicate that the effective mass of electrons parallel to the quantum wires is about 1.45 times as large as that of bulk GaAs. This increased effective mass reduces the electron mobility of the quantum wire at low temperature compared to the value which has been expected.