In this paper, a new open-ended microwave oven with E-field uniformity has been proposed for microelectronics packaging curing. The open-ended oven contains three dielectrics and an air-filled section, being physically open at one end but electrically shielded due to the evanescent mode in the air-filled section. The first, second, and third dielectrics are square, square, and ring-shaped, respectively. The relative permittivities of them are 2.1, 6.6, and 20.6, respectively. The first dielectric is used for a TM 11 mode cavity. The second and third dielectrics serve as impedance transformers for the entire face and the edge face, respectively. The second and third dielectrics, shifting the field along a longitudinal direction, increase the E-field intensities in the center region and perimeter region, respectively, on the external surface of the dielectric-air interface. The combination of both second and third dielectrics can result in the E-field uniformity and maximization at the dielectric-open end. In simulated analysis, uniformities of 2.8%, 2.8%, and 2.7% for the TM 11(1st) , TM 11(2nd) , and TM 11(3rd) modes were obtained, which are 7.6, 7.9, and 9.3 times better, respectively, than those of the conventional open-ended oven. The E-field uniformity was verified through experimental tests in two cases.