A semi has far fewer moving parts and most of them are protected inside the gun. Especially with striker fired guns. Revolvers have far more moving parts, many of which are exposed to the elements where ice, mud and debris can more easily mess thing up.
100 years of military field testing has clearly shown semi-auto pistols hold up to harsh conditions and abuse far better than revolvers. Kept clean and used in normal conditions a revolver will be slightly more reliable.