The Java-Web computing paradigm has changed the Internet into a computing environment. For Java-Web computing and many Java applications, a new Java processor called simultaneous multithreaded (SMT) JavaChip, is proposed to enhance the performance of previous Java processors by hardware support of Java multithreading. SMT JavaChip is a modified architecture with the enhanced mechanism of stack cache, instruction cache, functional units, etc. It executes dual independent threads simultaneously and enhances instruction level parallelism. The performance of SMT JavaChip is evaluated through the simulation using JavaSim, a Java processor simulator. This research is focused to enhance the performance of the Java processor by considering the characteristics of the Java language and computation environment. Performance results show that SMT JavaChip can provide an execution speedup of between 1.28 and 2.00 compared with the single threaded Java processors.