The quasi-bound levels in biased/unbiased double/triple-barrier quantum structures have been exactly calculated based on the solution of the one_dimensional (1D) time-independent Schrdinger equation using Airy function and transfer matrix method, which is easily extended to multi-barrier quantum structures; furthermo re, the dependence of the quasi-bound levels on the effective masses and bias in biased/unbiased double/triple-barrier quantum structures has also been investig ated. In addition, errors of Airy function and transfer matrix method in the stu dy of quasi-bound levels of biased multi-barrier quantum structures in other let ters have been pointed out and verified.