bachillerato = high school

Very often, educational terms turn out not to mean what you expected, and this is an example. "Bachillerato semestralizado" looks as though it ought to refer to the school year being divided into semesters, but that's not what it refers to in Colombia. "Semestralizado" means that (in principle) students at such a school do a whole year in a semester, so they do two years in one. They go at double the normal pace. So it involves what is generally called accelerated learning or education. This term normally applies to providing the facilities for gifted students to progress faster, but in Colombia it's more a matter of allowing those who have missed schooling to catch up more quickly. Here's an explanation:

"Bachillerato semestralizado, curse y reduzca la mitad de su tiempo de formación
Así como lo lee, ahora usted puede cursar su bachillerato semestralizado, reducir considerablemente su tiempo de formación, al tiempo que duplica otro tanto en actividades laborales o estudiar simultáneamente diplomados o cursos cortos. Cursando dos grados en un año, puede ahorrar muchísimo tiempo y prepararse para presentar las pruebas de estado en mucho menos de lo que la formación tradicional lo hace. [...]
Con la cantidad de estudiantes que se gradúan de los institutos de educación media y cursan sus estudios en seis años ¿no cree que pueda ser una buena idea reducir ese tiempo a la mitad estudiando su bachillerato semestralizado?"
https://www.slideshare.net/freddygarciafundetec/bachillerato...

"Do you know an expression to say in English "Bachillerato Semestralizado". I dont know if this sysyem does exist in the States or in the UK, but in Colombia there are certain institutions where people can get the high school degree faster than usual, attending to 2 grades in a year"
https://forum.wordreference.com/threads/bachillerato-semestr...

This is from a USAID document and refers to Colombia:

"Some 6,778 teachers have been trained to lead accelerated learning classes that allow students to complete two grades per year."
https://www.gpo.gov/fdsys/pkg/CHRG-109shrg39104149/pdf/CHRG-...

And this is also on Colombian education:

"more than 27,000 students were enrolled in the accelerated learning model, which gives students aged 10 to 17 who did not have the opportunity to enrol in basic education access to schooling."
https://oxfordbusinessgroup.com/overview/pillar-strength-sec...

"Bachillerato" in Colombia is the equivalent of the high school diploma: the final secondary qualification, but it also refers, as my reference above indicates, to all six years of secondary education:

"El bachillerato académico tiene una duración total de seis años y se divide en dos etapas; una de cuatro años (básica) y otra de dos años llamada media vocacional."
http://www.oei.es/historico/quipu/colombia/col09.pdf

So it's equivalent, really, to US high school, not just senior high.

I think "accelerated" is really the only way to get the meaning across; I can't see a way of doing it literally, using the word "semester", so that people who don't know the Colombian system will understand what it's about. It would be a good idea to add a note of explanation, if possible.