Apparatus having a plurality of strings of series-connected memory cells, and methods of their operation, where each of the strings of series-connected memory cells is selectively connected to the same data line through a respective plurality of select gates connected in series between that string and the data line. One select gate of each of the pluralities of select gates has a threshold voltage within a first range of threshold voltages, and each remaining select gate of each of the pluralities of select gates has a threshold voltage within a second range of threshold voltages mutually exclusive from the first range of threshold voltages. Each of the select gates having a threshold voltage within the first range of threshold voltages has its control gate isolated from any of the other select gates having a threshold voltage within the first range of threshold voltages.