Design Excellence | Collaboration | Innovation | Sustainability

These are the principles that YEI Engineers, Inc. was founded upon when established in 1975. Headquartered in Oakland, with branch offices in San Francisco and San Jose, YEI specializes in mechanical, electrical, and plumbing engineering for municipal, institutional, commercial, educational, and federal projects.

We pride ourselves on being excellent listeners and being highly responsive to our clients’ needs. We believe this is accomplished through senior-level involvement in all our projects. YEI produces creative and cost-effective engineering solutions with on-time delivery. We offer flexible designs to enhance usable space and to provide support during the construction administration phase. While we are a small business entity, we bring the project expertise and experience of a larger firm to bear on every job.


Moon H. Yuen, P.E., an Electrical Engineer, formed Yuen's Engineering Company as a sole proprietorship in August of 1975 in San Francisco, CA. Prior to founding his own company, Moon worked for Bechtel for twenty-seven years where he completed hundreds of design engineering projects. Some of his work was summarized in eighteen important technical papers including the low voltage heating of motors for which he was awarded a U.S. patent. "Short Circuit ABC," the most well-known of his technical papers were published in 1973. Throughout his professional career, Moon was a dedicated educator. He organized and taught numerous seminars and classes, which included the powerful MVA method. In 1991, Moon was elected a Fellow of the Institute of Electrical and Electronic Engineers (IEEE) and was recognized for his "contributions to electrical distribution system analyses and synthesis including the development of simplified methods of determining system transient conditions".

In October of 1975, Moon hired Weston Fenner, P.E. and in January of 1976, the two engineers formed a partnership called Yuen-Fenner and Associates. In August of 1977, the partnership was dissolved in favor of the corporation and became Yuen-Fenner, Inc. In October of 1977, Douglas Yung, P.E., formerly with PG&E and Bechtel, was invited to join the firm as a Director.

In March of 1980, both electrical and mechanical engineering services were offered with the addition of Harding Jung, P.E., Mechanical Engineer to the firm. In 1981, the company relocated its headquarter to Hayward, CA making the San Francisco location a branch office. With the departure of Weston Fenner from the firm in 1983, the former corporate name of Yuen-Fenner, Inc. was changed to YEI Engineers, Inc. (YEI) in March 1984.

In 1988, YEI’s Board of Directors elected Douglas Yung as President. In 2013, the Board elected Patrick Mallillin as President and George Cheung as Executive Vice President. 

Today, the firm is headquartered in Oakland, with branch offices in San Francisco and San Jose. The firm has over 20 electrical, mechanical, technical, and administrative staff professionals. In addition, over 30 technical papers and articles have been written and published by our engineers in professional publications, trade magazines, and technical journals.

YEI continues to provide reliable, practical, and high-quality MEP engineering design services.