1. A speech recognition circuit comprising: input means for receiving processed speech parameters; lexical memory means containing lexical data for word recognition, said lexical data comprising a plurality of lexical tree data structures, each lexical tree data structure comprising a model of words having common prefix components, an initial component of each lexical tree data structure being unique; a plurality of lexical tree processors connected in parallel to said input means for processing the speech parameters in parallel to perform parallel lexical tree processing for word recognition by accessing said lexical data in said lexical memory means; results memory means connected to said lexical tree processors for storing processing results from said lexical tree processors and lexical tree identifiers to identify lexical trees to be processed by said lexical tree processors; and control processor means for controlling said lexical tree processors to process lexical trees identified in said results memory means by performing parallel processing on a plurality of said lexical tree data structures.