Elliptic curve cryptography (ECC) provides the same security with shorter key lengths in comparison with other asymmetric cryptography algorithms. One of the safest curves recently considered is the Edwards25519, which is standardized by NIST. The most expensive operation in the ECC is point multiplication, which uses field multiplication many times. In this paper, a high-speed field multiplication for Edwards25519 is proposed. The improvements are mostly the result of the development of a novel semi-systolic field multiplier which employs four steps of Karatsuba-Ofman multiplication with fewer additions/subtractions in comparison with the original ones. The proposed multiplier has four register layers in its architecture. Then, this architecture, while taking advantage of the systolic architecture (a low CPD), has a low latency. In comparison with the best previous work, the proposed field multiplication has a 28% improvement in speed. Moreover, the point multiplication which exploits the proposed field multiplication has a 50% improvement in time in comparison with the best previous work.