Scheduling of threads based on the concept of thread essence is proposed in this paper. Multithreaded applications contain serial phases (single thread) and parallel phases (many threads). We propose a thread assignment mechanism that takes into account the essence of the threads in simultaneously-running applications that grants higher priority to applications during their criticalserial phases, for environments where there are more threads than cores. Furthermore, our proposed scheduler considers the limited resources of the system by reducing the number of context switches when there are more ready threads than cores. Analytic and experimental evaluation of the proposed thread assignment mechanism on both symmetric and emulated asymmetric multiprocessors show throughput improvements by as much as 16%, improved fairness by as much as 26% and reduced jitter by as much as 88%.