Pros
Interesting co-workers, since workforce is very highly educated and very international. Very challenging work, because of cutting-edge technology requirements and a global operational scope. Many people have worked there for more than a decade, and people who left often decide to come back to work there later. The company is large and diverse enough that you can grow your career without leaving the company. It also offers a wide variety of internal and external training options to help people keep growing their skills. The management is very disciplined about keeping money in the bank and being prepared for anything. Most products are #1 or #2 in their category. Just about any computer chip anywhere has made many trips through KLA-Tencor equipment during manufacturing. KLA-Tencor is also diversifying into related measurement applications, such as solar and LED manufacturing equipment. It's satisfying to work for a company that is a major exporter from the US, and which makes products which are tangible, highly complex, industry-leading, and necessary for the progress of the industries it serves.
Cons
The semiconductor capital equipment industry is very cyclical. While KLA-Tencor has tried to structure itself to minimize the impact, inevitably in up times the company grows, and in down times the company lays off people. It's a demanding industry with demanding deadlines. Hours can be long. Meetings can be at inconvenient times due to globalization. The corporate culture is oriented to techies and drivers, some people would feel it's impersonal and tough. Employees are constantly being asked to adapt and change, and do more with less. Standing still in this industry would quickly lead to decline.