Though the size of the system is getting larger towards exa-scale computation, the amount of available memory on computing nodes is expected to remain the same or to decrease. Therefore, memory efficiency is becoming an important issue for achieving scalability. This paper pointed out the problem of memory-inefficiency in the de-facto standard parallel programming model, Message Passing Interface (MPI). To solve this problem, the channel interface was introduced in the paper. This interface enables the programmers to appropriately allocate and de-allocate channels so that the program consumes just-enough amount of memory for communication. In addition to that, by limiting the message transfer supported by a channel as simple as possible, the memory consumption and the overhead for handling messages with this interface can be minimal. This paper showed a sample implementation of this interface. Then, the memory efficiency of the implementation is examined by the models of the memory consumption and the performance.