Going abroad with the EHIC
The European Health Insurance Card (EHIC) also replaces the former form E128 for students and "posted workers" who stay in another state for a longer, but limited period of time, and neither have their main residence there nor are they insured due to employment. In both cases, it is recommended to consult the domestic sickness insurance organisation before the departure as there are several deadlines that need to be considered.
For a semester abroad in a state that is not part of the EHIC system, a complementary insurance is highly recommended; not least because in some countries, the costs for medical treatments are much higher than in Austria (e.g. USA). Even if you submit the invoice afterwards, you might have to pay a significant differential amount.