Receptive process theory provides a semantic model for reasoning about nput/output-systems in general, and about the switching behaviour of asynchronous circuits in particular. As in the failures/divergences model of Hoare?s CSP, nondeterministic behaviour, as might result from the use of arbiters and synchronizers, can be modelled. A new result is the identification of the class of deterministic receptive processes, which is closed under composition. The defining characteristic of the class is that the behaviour of its members can be adequately described using a traces/divergences model. The closure of the class is proved with respect to a binary, parallel composition operator which allows inputs to be forked isochronically to both components and which conceals those outputs of either component that are inputs to the other component. This result contrasts with CSP, in which determinacy is not preserved when events are concealed.