A test array structure includes a substrate, first and second cells, first and second bit-line rings and four word-lines. Each of the first and second cells has a first drain region, a first gate region, a source region, a second gate region and a second drain region connected together in sequence. The first drain region and the first gate region of the first cell are located within the first bit-line ring. The second drain region and the second gate region of the first cell are located between the first and second bit-line rings. The first drain region and the first gate region of the second cell is located within the second bit-line ring. The second drain region of the first cell and the first drain region of the second cell are located between the two immediately-adjacent word-lines.