You don't have to split twice. Perl is smart enough to know how to load a flat list into a hash.

use strict;
use warnings;

use Data::Dumper;

my $string = "1:one;2:two;3:three";

my %hash = split /[;:]/, $string;

print Dumper \%hash;
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The output is:

$VAR1 = {
    '1' => 'one',
    '3' => 'three',
    '2' => 'two'
    };
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No guarantees as to the order, as hashes aren't sorted.