Disclosed are a semi-sequential Galois field GF(2n) multiplier and the method thereof. The GF(2n) multiplier comprises two ground field multipliers over GF(2m), at least a constant multiplier, and multiple GF(2m) adders. The high-order and low-order elements from a composite field GF((2m)2) for one operand of one GF(2n) multiplication are inputted in parallel into the two ground GF(2m) multipliers, respectively. The high-order and low-order elements from the composite field of another operand of the GF(2n) multiplication are sequentially inputted into the two ground GF(2m) multipliers. As such, multiple partial products are generated. The constant multiplication and additions are performed on the multiple partial products through the constant multiplier and the GF(2m) adders. This generates a high-order element and a low-order element of the composite field GF((2m)2). After mapping these two elements of GF((2m)2) back to GF(2n), the GF(2n) multiplication is done.