A semiconductor structure includes an alternating stack of insulating layers and electrically conductive layers, where the electrically conductive layers include word line electrically conductive layers and a first select-level electrically conductive layer, a memory opening vertically extending through the alternating stack, and a memory opening fill structure located in the memory opening and including a memory film and a vertical semiconductor channel. A vertical cross-sectional profile of an outer sidewall of the vertical semiconductor channel is straight throughout the word line electrically conductive layers and contains a lateral protrusion at a level of the first select-level electrically conductive layer.