Coherent spin dynamics of electrons laterally confined in a wide GaAs quantum well using a special mosaic electrode deposited onto the sample plane has been investigated. Electron spin lifetime measurements have been carried out in structures with different sizes of orifices in the mosaic electrode using the time-resolved Kerr rotation technique. It has been found that the electron spin lifetime in the lateral traps increases significantly with decreasing orifice size in the mosaic electrode. The observed electron spin lifetime dependence can be interpreted in terms of D'yakonov–Perel' spin relaxation mechanism suppression.