The seeding heuristic is widely used in many DNA analysis applications to speed up the analysis time. In many applications, seeding takes a substantial amount of the total execution time. In this paper, we present an efficient GPU implementation for computing maximal exact matching (MEM) seeds in long DNA reads. We applied various optimizations to reduce the number of GPU global memory accesses and to avoid redundant computation. Our implementation also extracts maximum parallelism from the MEM computation tasks. We tested our implementation using data from the state-of-the-art third generation Pacbio DNA sequencers, which produces DNA reads that are tens of kilobases long. Our implementation is up to 9x faster for computing MEM seeds as compared to the fastest CPU implementation running on a server-grade machine with 24 threads. Computing suffix array intervals (first part of MEM computation) is up to 3x faster whereas calculating the location of the match (second part) is up to 9x faster. The implementation is publicly available at https://github.com/nahmedraja/GPUseed.