Doesn't terminate correctly after int 20h?

Question

assembler

The program in afdpro displays a message - "Hello world!", and does not terminate correctly after the instruction int 20h (invalid opcode), so it can work, just wondering what's wrong?

CSEG segment
assume CS:CSEG, DS:CSEG, ES:CSEG, SS:CSEG
org 100h

Begin:
  mov ax,9
  mov dx,offset Message
  int 21h

  int 20h

 Message db 'Hello, world!$'
CSEG ends
end Begin

(after this
int 20
command, this command is executed:
db fe
these commands are executed correctly with their registers.)
Then all registers and segments are mixed up in
pusha and all sorts of catastrophes .. and
invalid opcode ..

Answer 1

Does it compile to .com or to .exe ? int 20h to exit is good only for .com , for .exe you should use

mov ax, 4c00h
int 21h