A three-dimensional memory device includes a first alternating stack of first word lines and first insulating layers, first memory stack structures vertically extending through the first alternating stack, a second alternating stack of second word lines and second insulating layers, second memory stack structures vertically extending through the second alternating stack, plural backside trench fill structures located between the first alternating stack and the second alternating stack, and a bridge region located between the plural backside trench fill structures and between the between the first alternating stack and the second alternating stack. At least one insulating layer extends continuously through the first alternating stack, the second alternating stack, and the bridge region.