The Microelectronics WebLab at MIT allows students to do actual (not simulated) laboratory research on state-of-the art equipment through the Internet. This study assesses the use of WebLab in a junior-level course on microelectronic devices and circuits in 2004-05 and 2005-06. In quantitative surveys and qualitative interviews, students and faculty reported that WebLab was effective as an instrument of learning, and grew more so with refinements of the program. WebLab allowed undergraduates to learn at their own pace and on their own schedules. It enabled them to use different processes of learning (intuitive, visual, abstract), and it gave them an opportunity to link individual and collaborative effort in creative combinations. Online laboratories on this model have broad applications in the experimental sciences and in other research-oriented disciplines.