In Spain it is essentially 30% of the salary (for standard salaries). Say the minimum is at least like 300€ (and you are not going to start a startup with 1000€ salaries.

Edit: that is: you have to pay the salary and, apart, 30% of that amount to the soc sec.

However in Spain you get an engineer for half the before-taxes salary compared to the US. Even if you add 30% it's still a lot cheaper.

Cost isn't the reason.

Depending on where in the US, even half is pushing it in most of Europe. For juniors, probably 20% of the cost of the US is more reasonable - especially in the 'startup land' of the Bay Area for example.

True, but when you're just starting out and you and your co-founders are the only employees you have a choice not to pay anything extra in US.

I don't envy US healthcare arrangement. The healthcare insurance is the only one of those compulsory taxes I don't mind here.

The difference is paid in taxes.