A vertical type semiconductor device can include a vertical pillar structure that includes a channel pattern with an outer wall. Horizontal insulating structures can be vertically spaced apart from one another along the vertical pillar structure to define first vertical gaps therebetween at first locations away from the outer wall and to define second vertical gaps therebetween at the outer wall, where the second vertical gaps are wider than the first vertical gaps. Horizontal wordline structures can be conformally located in the first and second vertical gaps between the vertically spaced apart horizontal insulating structures, so that the horizontal wordline structures can be vertically thinner across the first vertical gaps than across the second vertical gaps.