Magnetoresistance modulation, resulting from electron focusing, is investigated with multiparallel GaAs‐AlGaAs wires, which are defined by electron beam lithography and damageless wet‐chemical etching. Distinct focusing peaks in magnetoresistance are observed, although the samples have wires longer than a ballistic mean free path, which is derived from the focusing peak intensity. Specularity coefficientpfor the etched region boundary is also obtained asp≊1 from the focusing peak ratio. The mechanism limiting ballistic transport in the electron focusing condition is discussed, based on the temperature and the electron density dependence of the peak intensity.