Lateral quantization of the electronic motion in narrow (width < 200 nm) inversion channels is verified by direct spectroscopy of intersubband resonance transitions between quasi-one-dimensional subbands at infrared frequencies. Experimental results are discussed for periodical multichannel devices prepared as both GaAs/AlGaAs heterojunctions and Si MOS structures. In both cases crossover from one-dimensional to two-dimensional behavior can be observed via the variation of the surface potention.