A read operation for a memory device is provided. A selected word line, first and second global bit line groups and a selected first bit line group are precharged. A first cell current flowing through the selected word line, the first and the selected first bit line groups is generated. A first reference current flowing through the second global bit line group is generated. A first half page data is read based on the first cell current and the first reference current. The selected word line, the first and the second global bit line groups are kept precharged.