@nneuland i’d think you have two options there.
a) you check your router if you can find an option to “always assigned same IP” (or as sdetweil said a ‘reservation’
b) you configure your pi to not use DHCP but a static IP. If you have a VNC to your pi at the moment it should be easy to change the settings with the help of google.
Note that if you assign a static IP to your pi you might get into trouble if your router is configured as DHCP-server and tries to give this IP to someone other in your network. I’ve configured my Fritz!Box to use a DHCP scope from .100 - .254 so i have an own range for static ip’s whenever i need them. But i’m not sure if this is doable with your router. Best advice if you go this way, give the rpi a high number like >200, so it’s less likely some other connection will be assigned with that address

btw: @sdetweil something like a ‘static dhcp’ does not exist. you either use DHCP or static ;)