There are many variables…cost, how competitive, etc. Many colleges have programs about a week in length that are not too expensive (or even free). Their focus is often to expose the students to one of the STEM areas at their college…and probably to “sell” their school to the student as well. A couple examples for engineering are the University of Alabama Huntsville BEST (Be An Engineering Student) program (6 days, $300 instate, $600 OOS - but do give some scholarships), or the Auburn Sr. Tigers Camp (6 days, $695). There are also programs that are VERY expensive as well.
This camp is longer than what you are looking for, but I still thought I would mention it. Ole Miss has a 4 week program ("Summer College for High School Students -SCHS) that costs about $2000, but if your stats are high enough you automatically get a full scholarship. Their program has many options to choose from where you can take 2 classes for those 4 weeks, or there are some research opportunities that are available instead of taking the classes.
We found it valuable to try summer programs…it gave our kids exposure to residential life on a college campus, experience being away from home (and across the country), and exposure to a field they were interested in.
There is no comprehensive list that I have found, just do some google searches. Also look at individual colleges that have STEM majors, and search those for summer programs for high schoolers. As my S16 applies to colleges this fall, I have even stumbled across some options while perusing websites. You have to take some time and dig in order to find programs - but they are there!