from my experience in semiconductor fabs, its probably worth differentiating the different schedules a little bit. I'm going to start from generally the lowest to the highest paid while noting this doesn't necessarily reflect the lowest to highest value.

The factory: runs 24x7x365 - it has to, most processes have enough controlled time processes that it is a effectively week (or weeks) long process to shut down certain steps in the factory. Note for this whole comment I'm speaking of a typical 300mm high output FAB from a couple of years ago when I left the industry...for mental health/work life balance reasons. The reality is, if a single piece of critical equipment is down, it doesn't matter who you are, you will be on the phone, computer, or in the factory if your services are needed. During new process qualification it is not unheard of for equipment/process engineers to be expected to be at their equipment when certain special FOUPs of wafers are run - day or night.

The operators: typically 12ish hour shifts. Really 12 hours with an extra 15-30 min at the end to do an effective handover of the current situation of the fab. Typically in US fabs from my experience these are 3on 4off 4 on 3off schedules, often with wednesday or saturday/sunday as the swing day. In the olden days, these folks physically moved wafers and wafer boxes about the factory and it was a menial, fairly low skill, but highly precise job. Nowadays, most of them are sitting in some form of ops center monitoring looking at screens - because they are an unnecessary contaminant in the FAB. Due to automation, their number has gone down but their value and cognitive ability has definitely gone up because they are looking at the state of many pieces of equipment and many steps in the factory in an abstract way on a computer screen and controlling the movement of thousands of wafers and millions of dollars simultaneously. Good ones seem like they can see the future and are worth at least their weight in silver. I spent a lot of time trying to turn what the good ones saw/observed intuitively into systems, metrics, and control logic - that was cool and humbling.

The technicians: typically 12hour ish shifts 3 on 4 off unless doing cross training or something - with the same handover process that might last a little longer if they need to show something in person or show engineers something. These are the people physically working on the equipment by hand to perform preventative maintenance and repairs. These are the guys in the bunnysuits in the fab. Basically like the PhD version of a car mechanic. Good ones are paid more than a lot of the engineers - and are worth every cent. Beloved by ex navy folks (especially navy nukes and air force enlisted) - I knew of a fab in the North Eastern US where something like 16 techs 'hot bunked' in a nearby 2 bedroom apartment, 4 per shift, 4 shifts per week. Made local rent incredibly cheap and let them live somewhere else further away and nicer the remainder of the time.

The equipment/shift engineers: Half step between technicians and the process/yield engineers. Responsible for making sure individual pieces of equipment and fleets of equipment 'work' - meaning on target, clean, reliable etc. These are most frequently the people who's life get eaten by the job. They are attached to a physical asset that must work 95-99%+ of the 24x7x365 day year. This is where a lot of young engineers start and there is serious churn in some fabs. Compared to a lot of engineering roles, these folks really need good communication skills but it isn't necessarily obvious up front because it looks like a highly technical job on the surface. You have to build good relationships with your techs or you will fail, and often that means putting your ass in the FAB, listening, wiping, cleaning up tools to establish respect and trust.

The process engineers/yield team: Baseline is 9ish-5ish M-F, in my personal experience more like 7:15 to 5:30ish with coverage on weekends and nights available by a smaller group - not dissimilar to SREs in cloud companies. Its not that they don't work long hours, but they are not (generally) not on call as much or attached to a single physical asset.

Managers: work schedule unknown, except they are always there when you don't want them to be and never there when you wish they were :). Many of these roles become 'always available' roles, or historically they have been...some places have made moves to put two-in-a-box management models which seems to help burnout. I never did it officially but did a lot of coverage of these roles. It's kind of like air traffic control on + engineering + strategic planning mixed together.

Bigger picture - not everyone operates on the same schedule, because of the work they do and a variety of other factors. All of this is also dependent on when the 12/24 hour shifts start and end - some might run 7-7, others 8-8 or even 9-9. The exact shifts seem to shift FAB to FAB/company to company along with the boundaries of these roles. Production is different from 'ramp' is different from process development is different from R&D. What has seemed pretty universal is long hours for 'engineering types' who are doing the knowledge work and first level management of the factories physical assets. But long hours along with expectations for in person/on the phone/offline vary with a number of factors.

Would the FABS be better off with a larger workforce and a better work-life balance? My US/Euro work background perspective says yes - but I would also acknowledge there becomes, over time a huge amount of innate and tacit knowledge in these jobs that are highly experientially developed and just training more people is really hard. Coordinating amongst a larger group is even harder. That being said, I know a number of FABS that are really trying to push towards 'teams' of engineers that can slide and cross cover because the work life balance really can suck.

When I say suck I mean like (1) 'therapists near the plant who's entire patient list works for the FAB because its easier on the therapist and they still have a waiting list' sucks. And (2) 'people married to other FAB employees or single career households have longer lasting marriages' sucks.